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Reduce allocations while unfiltering by reusing buffers

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This commit is contained in:
Kamal Ahmad 2019-08-11 14:53:06 +05:00
parent 1a6284b177
commit e04153051c
2 changed files with 27 additions and 25 deletions
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42
src/filters.rs
View file

@ -62,30 +62,31 @@ pub fn filter_line(filter: u8, bpp: usize, data: &[u8], last_line: &[u8], buf: &
} }
} }
pub fn unfilter_line(filter: u8, bpp: usize, data: &[u8], last_line: &[u8]) -> Vec<u8> { pub fn unfilter_line(filter: u8, bpp: usize, data: &[u8], last_line: &[u8], buf: &mut Vec<u8>) {
let mut unfiltered = Vec::with_capacity(data.len()); assert_eq!(buf.len(), 0);
buf.reserve(data.len());
match filter { match filter {
0 => { 0 => {
unfiltered.extend_from_slice(data); buf.extend_from_slice(data);
} }
1 => { 1 => {
for (i, byte) in data.iter().enumerate() { for (i, byte) in data.iter().enumerate() {
match i.checked_sub(bpp) { match i.checked_sub(bpp) {
Some(x) => { Some(x) => {
let b = unfiltered[x]; let b = buf[x];
unfiltered.push(byte.wrapping_add(b)); buf.push(byte.wrapping_add(b));
} }
None => { None => {
unfiltered.push(*byte); buf.push(*byte);
} }
}; };
} }
} }
2 => { 2 => {
if last_line.is_empty() { if last_line.is_empty() {
unfiltered.extend_from_slice(data); buf.extend_from_slice(data);
} else { } else {
unfiltered.extend( buf.extend(
data.iter() data.iter()
.zip(last_line.iter()) .zip(last_line.iter())
.map(|(cur, last)| cur.wrapping_add(*last)), .map(|(cur, last)| cur.wrapping_add(*last)),
@ -97,23 +98,23 @@ pub fn unfilter_line(filter: u8, bpp: usize, data: &[u8], last_line: &[u8]) -> V
if last_line.is_empty() { if last_line.is_empty() {
match i.checked_sub(bpp) { match i.checked_sub(bpp) {
Some(x) => { Some(x) => {
let b = unfiltered[x]; let b = buf[x];
unfiltered.push(byte.wrapping_add(b >> 1)); buf.push(byte.wrapping_add(b >> 1));
} }
None => { None => {
unfiltered.push(*byte); buf.push(*byte);
} }
}; };
} else { } else {
match i.checked_sub(bpp) { match i.checked_sub(bpp) {
Some(x) => { Some(x) => {
let b = unfiltered[x]; let b = buf[x];
unfiltered.push(byte.wrapping_add( buf.push(byte.wrapping_add(
((u16::from(b) + u16::from(last_line[i])) >> 1) as u8, ((u16::from(b) + u16::from(last_line[i])) >> 1) as u8,
)); ));
} }
None => { None => {
unfiltered.push(byte.wrapping_add(last_line[i] >> 1)); buf.push(byte.wrapping_add(last_line[i] >> 1));
} }
}; };
}; };
@ -124,25 +125,25 @@ pub fn unfilter_line(filter: u8, bpp: usize, data: &[u8], last_line: &[u8]) -> V
if last_line.is_empty() { if last_line.is_empty() {
match i.checked_sub(bpp) { match i.checked_sub(bpp) {
Some(x) => { Some(x) => {
let b = unfiltered[x]; let b = buf[x];
unfiltered.push(byte.wrapping_add(b)); buf.push(byte.wrapping_add(b));
} }
None => { None => {
unfiltered.push(*byte); buf.push(*byte);
} }
}; };
} else { } else {
match i.checked_sub(bpp) { match i.checked_sub(bpp) {
Some(x) => { Some(x) => {
let b = unfiltered[x]; let b = buf[x];
unfiltered.push(byte.wrapping_add(paeth_predictor( buf.push(byte.wrapping_add(paeth_predictor(
b, b,
last_line[i], last_line[i],
last_line[x], last_line[x],
))); )));
} }
None => { None => {
unfiltered.push(byte.wrapping_add(last_line[i])); buf.push(byte.wrapping_add(last_line[i]));
} }
}; };
}; };
@ -150,7 +151,6 @@ pub fn unfilter_line(filter: u8, bpp: usize, data: &[u8], last_line: &[u8]) -> V
} }
_ => unreachable!(), _ => unreachable!(),
} }
unfiltered
} }
fn paeth_predictor(a: u8, b: u8, c: u8) -> u8 { fn paeth_predictor(a: u8, b: u8, c: u8) -> u8 {

10
src/png/mod.rs
View file

@ -282,17 +282,19 @@ impl PngImage {
let bpp = ((self.ihdr.bit_depth.as_u8() * self.channels_per_pixel() + 7) / 8) as usize; let bpp = ((self.ihdr.bit_depth.as_u8() * self.channels_per_pixel() + 7) / 8) as usize;
let mut last_line: Vec<u8> = Vec::new(); let mut last_line: Vec<u8> = Vec::new();
let mut last_pass = 1; let mut last_pass = 1;
let mut unfiltered_buf = Vec::new();
for line in self.scan_lines() { for line in self.scan_lines() {
if let Some(pass) = line.pass { if let Some(pass) = line.pass {
if pass != last_pass { if pass != last_pass {
last_line = Vec::new(); last_line.clear();
last_pass = pass; last_pass = pass;
} }
} }
let unfiltered_line = unfilter_line(line.filter, bpp, &line.data, &last_line); unfilter_line(line.filter, bpp, &line.data, &last_line, &mut unfiltered_buf);
unfiltered.push(0); unfiltered.push(0);
unfiltered.extend_from_slice(&unfiltered_line); unfiltered.extend_from_slice(&unfiltered_buf);
last_line = unfiltered_line; std::mem::swap(&mut last_line, &mut unfiltered_buf);
unfiltered_buf.clear();
} }
unfiltered unfiltered
} }